opticore/includes/class-lazy-loader.php

<?php
/**
 * Lazy Loader Class
 * 
 * Handles lazy loading for images and iframes
 */

if (!defined('ABSPATH')) {
    exit;
}

class OptiCore_Lazy_Loader {
    
    private static $instance = null;
    
    public static function get_instance() {
        if (null === self::$instance) {
            self::$instance = new self();
        }
        return self::$instance;
    }
    
    private function __construct() {
    }
    
    public function init() {
        // Add lazy loading to images
        add_filter('the_content', array($this, 'add_lazy_loading'), 999);
        add_filter('post_thumbnail_html', array($this, 'add_lazy_loading'), 999);
        add_filter('get_avatar', array($this, 'add_lazy_loading'), 999);
        
        // Add loading attribute to images (native lazy loading)
        add_filter('wp_get_attachment_image_attributes', array($this, 'add_loading_attribute'), 10, 3);
        
        // Enqueue lazy load script if needed
        add_action('wp_enqueue_scripts', array($this, 'enqueue_scripts'));
    }
    
    /**
     * Add lazy loading to content
     */
    public function add_lazy_loading($content) {
        if (is_admin() || is_feed() || is_preview()) {
            return $content;
        }
        
        // Add loading="lazy" to images
        $content = preg_replace_callback(
            '/<img([^>]+)>/i',
            array($this, 'add_lazy_to_image'),
            $content
        );
        
        // Add lazy loading to iframes
        $content = preg_replace_callback(
            '/<iframe([^>]+)>/i',
            array($this, 'add_lazy_to_iframe'),
            $content
        );
        
        return $content;
    }
    
    /**
     * Add lazy loading to image tag
     */
    public function add_lazy_to_image($matches) {
        $img = $matches[0];
        
        // Skip if already has loading attribute
        if (strpos($img, 'loading=') !== false) {
            return $img;
        }
        
        // Skip if it's a data URI
        if (strpos($img, 'src="data:') !== false) {
            return $img;
        }
        
        // Add loading="lazy"
        $img = str_replace('<img', '<img loading="lazy"', $img);
        
        // Add decoding="async"
        if (strpos($img, 'decoding=') === false) {
            $img = str_replace('<img', '<img decoding="async"', $img);
        }
        
        return $img;
    }
    
    /**
     * Add lazy loading to iframe tag
     */
    public function add_lazy_to_iframe($matches) {
        $iframe = $matches[0];
        
        // Skip if already has loading attribute
        if (strpos($iframe, 'loading=') !== false) {
            return $iframe;
        }
        
        // Add loading="lazy"
        $iframe = str_replace('<iframe', '<iframe loading="lazy"', $iframe);
        
        return $iframe;
    }
    
    /**
     * Add loading attribute to images
     */
    public function add_loading_attribute($attr, $attachment, $size) {
        if (!isset($attr['loading'])) {
            $attr['loading'] = 'lazy';
        }
        
        if (!isset($attr['decoding'])) {
            $attr['decoding'] = 'async';
        }
        
        return $attr;
    }
    
    /**
     * Enqueue scripts
     */
    public function enqueue_scripts() {
        // Native lazy loading is supported in modern browsers
        // No additional JS needed for basic functionality
        
        // Optional: Add intersection observer polyfill for older browsers
        if ($this->needs_polyfill()) {
            wp_enqueue_script(
                'opticore-lazy-polyfill',
                OPTICORE_PLUGIN_URL . 'assets/js/lazy-load-polyfill.js',
                array(),
                OPTICORE_VERSION,
                true
            );
        }
    }
    
    /**
     * Check if polyfill is needed
     */
    private function needs_polyfill() {
        // Check user agent for older browsers
        $user_agent = isset($_SERVER['HTTP_USER_AGENT']) ? $_SERVER['HTTP_USER_AGENT'] : '';
        
        // Check for old browsers that don't support native lazy loading
        if (preg_match('/MSIE|Trident|Edge\/([0-9]{2})\./i', $user_agent)) {
            return true;
        }
        
        return false;
    }
    
    /**
     * Preload critical images
     */
    public function preload_critical_images() {
        // Get the featured image of the current post/page
        if (is_singular()) {
            $thumbnail_id = get_post_thumbnail_id();
            if ($thumbnail_id) {
                $thumbnail_url = wp_get_attachment_image_url($thumbnail_id, 'large');
                if ($thumbnail_url) {
                    echo '<link rel="preload" as="image" href="' . esc_url($thumbnail_url) . '">';
                }
            }
        }
    }
}